We recently added a new addition to our family - a little rescue puppy that we got at our local shelter. Our 3-year-old son was there when we picked out the pup and was excited when we brought the new pup home, but now he seems to be afraid. The puppy wants to play all the time and has a lot of energy, and it seems to be too much for our son to handle. What can we do to calm our son's fears?